Contents
About the Authors··ii
Preface··x
The Learning System··xii

Chapter 1
Introduction to Physical Geology··2

Who Needs Geology?··4

Avoiding Geologic Hazards··6
Supplying Things We Need··7
Protecting the Environment··8
Understanding Our Surroundings··11

An Overview of Physical Geology-Important Concepts··11

Internal Processes: How the Earth's Internal Heat Engine Works··14
The Earth's Interior··15
The Theory of Plate Tectonics··16
Surficial Processes: The Earth's External Heat Engine··18

Geologic Time··21

Summary··22

*These end-of-chapter sections appear in every chapter.

Terms to Remember*··23
Testing Your Knowledge*··23
Expanding Your Knowledge*··24
Exploring Resources*··24
Interacting with Journey Through Geology CD-ROM*··25

Chapter 2
Atoms, Elements, and Minerals··26

Atoms and Elements··28

Chemical Activity··30
Ions··30

Chemical Composition of the Earth's Crust··31

Crystallinity··32

The Silicon-Oxygen Tetrahedron··33

Minerals··37

Crystalline Solids··37
Natural and Inorganic Substances··37
Definite Chemical Composition··37
The Important Minerals··38

The Physical Properties of Minerals··40

Color··40
Streak··40
Luster··40
Hardness··40
External Crystal Form··41
Cleavage··43
Fracture··45
Specific Gravity··45
Other Properties··46
Simple Chemical Tests··46

The Rock Cycle··47

Summary··49

Chapter 3
Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks··52

Igneous Rocks··55

Identification of Igneous Rocks··55
Varieties of Granite··58
Chemistry of Igneous Rocks··58

Intrusive Bodies··59

Shallow Intrusive Structures··60
Intrusives That Crystallize at Depth··61

Abundance and Distribution of Plutonic Rocks··63

How Magma Forms··63

Heat for Melting Rock··64
Factors That Control Melting Temperatures··64

How Magmas of Different Compositions Evolve··66

Differentiation and Bowen's Reaction Theory··66
Partial Melting··68
Assimilation··69
Mixing of Magmas··69

Explaining Igneous Activity by Plate Tectonics··70

Igneous Processes at Divergent Boundaries··70
Intraplate Igneous Activity··70
Igneous Processes at Convergent Boundaries··71

Summary··73

Chapter 4
Volcanism and Extrusive Rocks··76

Effects on Humans··78
The Growth of Hawaii··78
Geothermal Energy··78
Effect on Climate··78
Volcanic Catastrophes··81
Eruptive Violence and Physical Characteristics of Lava··82

Extrusive Rocks and Gases··83

Scientific Investigation of Volcanism··83
Gases··84

Extrusive Rocks··84
Types of Volcanoes··87

Shield Volcanoes··88
Cinder Cones··88
Composite Volcanoes··90
Volcanic Domes··93

Lava Floods··95
Submarine Eruptions··96

Pillow Basalts··97

Summary··99

Chapter 5
Weathering and Soil··102

Weathering, Erosion, and Transportation··104
How Weathering Alters Rocks··104

Effects of Weathering··104

Mechanical Weathering··104

Frost Action··104
Abrasion··106
Pressure Release··107

Chemical Weathering··108

Role of Oxygen··108
Role of Acid··109
Solution Weathering··110
Chemical Weathering of Feldspar··111
Chemical Weathering of Other Minerals··112
Weathering and Climate··113
Weathering Products··113

Soil··113

Soil Horizons··114
Residual and Transported Soils··114
Soils, Parent Rock, Time, and Slope··115
Organic Activity··116
Soils and Climate··116
Buried Soils··117

Summary··118

Chapter 6
Sediments and Sedimentary Rocks··120

Sediment··122

Transportation··122
Deposition··123
Preservation··124
Lithification··125

Types of Sedimentary Rocks··126
Clastic Rocks··126

Breccia and Conglomerate··126
Sandstone··127
The Fine-Grained Rocks··128

Chemical Sedimentary Rocks··130

Carbonate Rocks··130
Chert··133
Evaporites··134

Organic Sedimentary Rocks··135

Coal··135

The Origin of Oil and Gas··135
Sedimentary Structures··135
Formations··139
Interpretation of Sedimentary Rocks··140

Source Area··140
Environment of Deposition··142
Plate Tectonics and Sedimentary Rocks··145

Summary··146

Chapter 7
Metamorphism, Metamorphic Rocks, and Hydrothermal Rocks··150

Factors Controlling the Characteristics of Metamorphic Rocks··152

Composition of the Parent Rock··152
Temperature··153
Pressure··153
Fluids··155
Time··156

Classification of Metamorphic Rocks··156
Types of Metamorphism··156

Contact Metamorphism··156
Regional Metamorphism··158

Plate Tectonics and Metamorphism··162
Hydrothermal Processes··163

Hydrothermal Activity at Divergent Plate Boundaries··163
Metasomatism··165
Hydrothermal Rocks and Minerals··166
Sources of Water··167

Summary··169

Chapter 8
Time and Geology··172

The Key to the Past··174
Relative Time··174

Principles Used to Determine Relative Age··174
Correlation··179
The Standard Geologic Time Scale··182

Unconformities··183

Disconformities··183
Angular Unconformities··185
Nonconformities··186

Numerical Age··186

Isotopic Dating··186
Uses of Isotopic Dating··190
Combining Relative and Numerical Ages··190
Age of the Earth··191
Comprehending Geologic Time··191

Summary··195

Chapter 9
Mass Wasting··198

Classification of Mass Wasting··200

Rate of Movement··200
Type of Material··200
Type of Movement··202

Controlling Factors in Mass Wasting··203

Gravity··204
Water··204

Common Types of Mass Wasting··205

Creep··205
Debris Flow··206
Rockfalls and Rockslides··212

Preventing Landslides··215

Preventing Mass Wasting of Debris··215
Preventing Rockfalls and Rockslides on Highways··216

Summary··218

Chapter 10
Streams and Floods··220

The Hydrologic Cycle··222
Channel Flow and Sheet Flow··222
Drainage Basins··224
Drainage Patterns··224
Factors Affecting Stream Erosion and Deposition··225

Velocity··225
Gradient··226
Channel Shape and Roughness··226
Discharge··227

Stream Erosion··228
Stream Transportation of Sediment··229
Stream Deposition··230

Bars··230
Braided Streams··231
Meandering Streams and Point Bars··235
Flood Plains··237
Deltas··239
Alluvial Fans··241

Flooding··242

Urban Flooding··242
Flash Floods··245
Controlling Floods··246
The Great Flood of 1993··247

Stream Valley Development··248

Downcutting and Base Level··248
The Concept of a Graded Stream··250
Lateral Erosion··251
Headward Erosion and Stream Piracy··251

Stream Terraces··252
Incised Meanders··253
Superposed Streams··255

Summary··255

Chapter 11
Ground Water··258

Porosity and Permeability··260
The Water Table··260
The Movement of Ground Water··262
Aquifers··263
Wells··264
Springs and Streams··266
Ground Water Contamination··266
Balancing Withdrawal and Recharge··272
Effects of Groundwater Action··274

Caves, Sinkholes, and Karst Topography··274
Other Effects··276

Hot Water Underground··277

Geothermal Energy··278

Summary··279

Chapter 12
Glaciers and Glaciation··282

The Theory of Glacial Ages··284
Glaciers-Where They Are, How They Form and Move··284

Distribution of Glaciers··284
Types of Glaciers··285
Formation and Growth of Glaciers··285
Movement of Valley Glaciers··288
Movement of Ice Sheets··293

Glacial Erosion··294

Erosional Landscapes Associated with Alpine Glaciation··295
Erosional Landscapes Associated with Continental Glaciation··298

Glacial Deposition··299

Moraines··300

Outwash··302

Glacial Lakes and Varves··303

Effects of Past Glaciation··303

The Glacial Ages··303
Direct Effects of Past Glaciation in North America··305
Indirect Effects of Past Glaciation··310
Evidence for Older Glaciation··310

Summary··311

Chapter 13
Deserts and Wind Action··314

Distribution of Deserts··316
Some Characteristics of Deserts··316
Desert Features in the Southwestern United States··319

Wind Action··322

Wind Erosion and Transportation··324
Wind Deposition··327

Summary··332

Chapter 14
Waves, Beaches, and Coasts··336

Water Waves··338

Surf··339

Nearshore Circulation··340

Wave Refraction··340
Longshore Currents··340
Rip Currents··341

Beaches··341
Longshore Drift of Sediment··342

Human Interference with Sand Drift··344
Sources of Sand on Beaches··344

Coasts and Coastal Features··344

Erosional Coasts··345
Depositional Coasts··348
Drowned Coasts··349
Uplifted Coasts··352
Coasts Shaped by Organisms··352

Summary··353

Chapter 15
Geologic Structures··356

Tectonic Forces at Work··358

Stress and Strain in the Earth's Crust··358
Behavior of Rocks to Stress and Strain··359
Present Deformation of the Crust··360

Structures as a Record of the Geologic Past··361

Geologic Maps and Field Methods··361

Folds··363

Geometry of Folds··363
Interpreting Folds··366

Fractures in Rock··367

Joints··368
Faults··370

Summary··379

Chapter 16
Earthquakes··382

Causes of Earthquakes··384
Seismic Waves··386

Body Waves··386
Surface Waves··386

Locating and Measuring Earthquakes··386

Determining the Location of an Earthquake··389
Measuring the Size of an Earthquake··390
Location and Size of Earthquakes in the United States··393

Effects of Earthquakes··395

Tsunamis··399

World Distribution of Earthquakes··401
First-Motion Studies of Earthquakes··404
Earthquakes and Plate Tectonics··404

Earthquakes at Plate Boundaries··405
Subduction Angle··408

Earthquake Prediction··408
Earthquake Control··409

Summary··411

Chapter 17
Earth's Interior and Geophysical Properties··414

Evidence from Seismic Waves··416
Earth's Internal Structure··417

The Crust··418
The Mantle··418
The Core··420

Isostasy··423
Gravity Measurements··425
Earth's Magnetic Field··427

Magnetic Reversals··428
Magnetic Anomalies··429

Heat Within the Earth··432

Geothermal Gradient··432
Heat Flow··433

Summary··433

Chapter 18
The Sea Floor··436

Origin of the Ocean··438
Methods of Studying the Sea Floor··439
Features of the Sea Floor··440
Continental Shelves and Continental Slopes··440
Submarine Canyons··442

Turbidity Currents··443

Passive Continental Margins··443

The Continental Rise··443
Abyssal Plains··444

Active Continental Margins··444

Oceanic Trenches··445

The Mid-Oceanic Ridge··445

Geologic Activity on the Ridge··446
Biologic Activity on the Ridge··446

Fracture Zones··449
Seamounts, Guyots, and Aseismic Ridges··449
Reefs··450
Sediments of the Sea Floor··452
Oceanic Crust and Ophiolites··452
The Age of the Sea Floor··454
The Sea Floor and Plate Tectonics··455

Summary··455

Chapter 19
Plate Tectonics··458

The Early Case for Continental Drift··460

Skepticism about Continental Drift··462

Paleomagnetism and the Revival of Continental Drift··463

Recent Evidence for Continental Drift··464
History of Continental Positions··465

Sea-Floor Spreading··465

Hess's Driving Force··466
Explanations··466

Plates and Plate Motion··467
How Do We Know That Plates Move?··468

Marine Magnetic Anomalies··468
Another Test: Fracture Zones and Transform Faults··471
Measuring Plate Motion Directly··472

Divergent Plate Boundaries··472
Transform Boundaries··475
Convergent Plate Boundaries··476

Ocean-Ocean Convergence··477
Ocean-Continent Convergence··478
Continent-Continent Convergence··480

Backarc Spreading··481
The Motion of Plate Boundaries··482
Plate Size··482
The Attractiveness of Plate Tectonics··482
What Causes Plate Motions?··483

Mantle Plumes and Hot Spots··486

The Relationship Between Plate Tectonics and Ore Deposits··488
A Final Note··492

Summary··492

Chapter 20
Mountain Belts and the Continental Crust··496

Characteristics of Major Mountain Belts··499

Size and Alignment··499
Ages of Mountain Belts and Continents··499
Thickness and Characteristics of Rock Layers··501
Patterns of Folding and Faulting··502
Metamorphism and Plutonism··504
Normal Faulting··504

Thickness and Density of Rocks··504

Features of Active Mountain Ranges··505

The Evolution of a Mountain Belt··505

The Accumulation Stage··505
The Orogenic Stage··506
The Uplift and Block-faulting Stage··509

The Growth of Continents··514

Suspect and Exotic Terranes··515

Summary··518

Chapter 21
Geologic Resources··520

Types of Resources··522

Resources and Reserves··523

Energy Use··523
Oil and Natural Gas··523

The Occurrence of Oil and Gas··524
Recovering the Oil··526
How Much Oil Do We Have Left?··527

Heavy Crude and Oil Sands··528
Oil Shale··528
Coal··529

Varieties of Coal··529
Occurrence of Coal··530
Environmental Effects··532
Reserves and Resources··532

Uranium··532
Alternative Sources of Energy··533
Metals and Ores··533
Origin of Metallic Ore Deposits··533

Ores Associated with Igneous Rocks··534
Ores Formed by Surface Processes··535

Metal Ores and Plate Tectonics··536
Mining··536

Environmental Effects··537

Some Important Metals··538

Iron··538
Copper··538
Aluminum··538
Lead··539
Zinc··539
Silver··539
Gold··539
Other Metals··540

Nonmetallic Resources··540

Construction Materials··540
Fertilizers and Evaporites··541
Other Nonmetallics··542
Some Future Trends··542

Summary··543

Appendixes A-G··546

Glossary··556

Index··569